Why does the dog still have proglottids in faeces? Apparent anthelmintic resistance of Dipylidium caninum in ‘Fuego’.

The latest Paper of the Month for Parasitology is First report of apparent praziquantel resistance in Dipylidium caninum in Europe and is freely available for one month. 

Helminth parasites have ruthlessly plagued human and animal hosts for centuries. Modern veterinary medicine has achieved a considerable milestone in controlling these pathogens primarily through the administration of anthelmintic drugs that are able to eradicate these unwelcome guests. However, just as bacteria can develop resistance to antibiotics, the emergence of anthelmintic resistance in helminth parasites has received increased attention in the last decades. And just as in bacterial infections, anthelmintic resistance can pose serious threats to animal health, welfare, and productivity and potentially extend to the human health sector as well.

Here, we present ‘Fuego’, a Can de Chira dog that was shedding proglottids of Dipylidium caninum – the flea tapeworm –  for months, despite repeated and correct anthelmintic treatments. Hence, the dog did not respond to treatment with praziquantel – the agent of choice – in a standard label treatment dose. And even though symptoms in ‘Fuego’ were mild (i.e., restlessness, squashy faeces), both patient and owners were stressed and suffered from the situation.

Eggs clustered in packets with hexacanth embryo typical for Dipylidium caninum, obtained from Fuego’s stool subjected to flotation.

‘Fuego’ had been born in Spain and then moved to Switzerland, where the shedding of proglottids and the clinical signs first occurred a few weeks after he had arrived in his new home. In Spain, Fuego had been treated with a compound containing praziquantel, febantel, and pyrantel. In Switzerland, treatment against fleas – the intermediate hosts – was ensured via appropriate medication and environmental measures ruling out re-infections, accompanied with a classical broad spectrum (praziquantel/pyrantel/febantel) anthelmintic. Praziquantel treatment was therefore included. Following a second treatment after 2 weeks, proglottid excretion was suspended indicating some efficacy. As proglottid excretion resumed after some weeks, praziquantel (combined with milbemycinoxime) was given in appropriate dose but then, due to lack of success, we suggested the administration of fenbendazole for 5 consecutive days. Our hope was shattered, with proglottid shedding ceasing for 4 days only. Several further treatments with praziquantel/milbemycin in narrow intervals were desperately attempted, yet without success.

At this stage, the international collaboration with veterinary parasitologists started. We first opted for epsiprantel, another compound normally efficacious against tapeworms, but not available in Switzerland. As this did not work either, we used mebendazole licensed in Italy and then tried another compound containing praziquantel/pyrantel/oxantel, expecting some synergistic effect. Eventually, we were successful with mebendazole for 5 days, administered in a higher dose despite potential side effects. These were not observed, but proglottid shedding and clinical signs finally stopped and the dog remained clean and in good health for more than 10 months. During the investigations, we heard of alleged lack of efficacy of praziquantel against D. caninum from colleagues in surrounding countries. However, this report represents the first published case of apparent praziquantel resistance in D. caninum in Europe. We do not fully understand the mechanisms of such resistances, but correct management of parasitic infections in companion animals, as they live very closely with humans, is paramount to prevent the further spread of anthelmintic resistance and zoonotic diseases. We were also confronted with a clear lack of treatment alternatives which we have overcome thanks to information from the literature and a network of colleagues across countries supporting the shipment of licensed medication from their countries.

‘Fuego’, a Can de Chira dog imported to Switzerland at the approximate age of 10 months of age. The dog was probably born in December 2021 around Monzón or Huesca (municipality of Aragon, Spain) and had been picked up from the street at the approximate age of four months together with other dogs of the same age. ‘Fuego’ was presented in a Swiss veterinary clinic with a history of chronic excretion of tapeworm proglottids; he presented general restlessness, tenesmus, slight anal pruritus, and occasionally squashy faeces.

Tapeworm proglottids at the surface of Fuego’s droppings. They were morphologically identified as Dipylidium caninum specimens. After several anthelmintic treatments, including praziquantel and epsiprantel, proglottid excretion only stopped after oral administration of 86.2 mg/kg body weight mebendazole for 5 days.

The paper First report of apparent praziquantel resistance in Dipylidium caninum in Europe by Andreas W. Oehm, Anton Reiter, Angela Binz and Manuela Schnyder, published in Parasitology, is available free for a month. 


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